When a signal is transmitted between two calculation control devices, a communication error can occur due to a sticking or the like of RAM of a communication buffer, in addition to a calculation error in the calculation control devices. With regard to such a problem, it is described in Japanese Patent Laid-open Publication Hei 6-298105 to construct the operation control device for vehicles such that two calculation control devices not only watch the results of calculation of each other but also watch an occurrence of an abnormality in the communication means therebetween by providing main and sub CPU therein and comparing the output of CPU of each other.